Re: How many fields in a table are too many

<btober(at)seaworthysys(dot)com> writes:
>> As long as we are playing "who's is biggest", I have one with 900+
>> attributes (normalized) but there is a big warning - if you have a
>> query that returns hundreds of columns it will be very, very slow.

> Is the SELECT * the only circumstance? That is, if you specify a small
> number of columns, does the response improve even though the table
> actually has that large number of columns but is only be asked to supply
> a column-limited result set?

IIRC, the worst problems that Steve's profile exposed were associated
with large numbers of columns in a SELECT result --- there are some
doubly nested loops that take time O(N^2) in the number of columns.
But I would not be surprised if some of those loops get invoked on the
underlying table, too, depending on what your query looks like exactly.

This is all eminently fixable, it's just a matter of someone finding
some round tuits ... for most people it doesn't seem like a
high-priority problem, since you won't notice it till you get into the
hundreds of columns ...

regards, tom lane